This invention relates generally to archery bows and more particularly to a riser of an archery bow.
Compound archery bows typically have a riser with a handle portion grippable by the user and a pair of limbs connected to the riser and extending from opposed ends of the riser with one or more strings trained around a cam at the free end of each limb. The risers are formed from a metal, such as aluminum, due to its strength to weight characteristics. The metal riser may be either extruded or cut from bar stock.
Attempts have been made to form risers of archery bows from carbon fiber or other composite materials. One method is a so-called xe2x80x9cresin transfer molding processxe2x80x9d in which fibers are placed loosely into a mold and under pressure a resin is injected into the mold. However, the loose fibers in the mold are displaced by the injected pressurized resin resulting in voids in the formed riser, dry fibers not saturated by resin and areas rich in resin but without sufficient fibers therein creating weak spots or voids in the riser. Attempts to fire an archery bow having such a riser quickly results in failure of the riser by cracking or other fracture. Particularly hazardous is the xe2x80x9cdry firingxe2x80x9d of a poorly formed polymeric riser due to the increased vibration and stresses on the bow. Such poorly formed composite risers fail quickly when dry fired. Further, loose, random positioning of fibers in the mold and the displacement of fibers due to the injection of the resin into the mold, results in very inconsistent parts from one riser to the next. Unfortunately, the structural integrity of any given riser is unknown, absent obvious deformations of flaws. Accordingly, the location of voids or resin rich areas vary from part to part and could not be readily detected until the bow was fired and failure, such as fracture of the riser, occurred.
A composite riser for an archery bow formed from fibers embedded in resin in such a way that resin rich areas, dry fibers and voids are eliminated, providing consistent risers of high quality. The location of structural fibers, such as a carbon fibers or fiberglass composite materials, is ensured within a mold used to form the riser and relative to the resin which bonds the fibers together. Various processes may be used to form the riser with control of the fibers and resin maintained. For example, structural reaction injection molding, liquid composite molding, continuous fiber molding, modified compression molding, resin transfer molding and variable infusion molding processes can be used.
Objects, features and advantages of this invention include providing an archery bow having a composite riser and a method of making the composite riser which eliminates resin rich areas, eliminates voids in the riser, eliminates dry fibers, provides consistent parts of high integrity, enables formation of the riser by a plurality of molding processes, controls the orientation and location of fibers in the mold, can produce a riser molded in substantially its final shape to reduce machining, reduces waste of material when forming the riser, may utilize unidirectional fibers, may utilize woven fiber sheets, may utilize filament winding processes, may utilize any combination of unidirectional fibers, woven fibers and filament winding processes, can utilize thermoplastic or thermoset resins, is reliable, durable and of relatively simple design and economical manufacture and assembly, and has a long useful life in service.